diff -r f9bc8cd4da8f src/org/python/compiler/ProxyMaker.java
--- a/src/org/python/compiler/ProxyMaker.java	Sat Jun 04 18:02:13 2011 -0700
+++ b/src/org/python/compiler/ProxyMaker.java	Wed Aug 24 20:15:13 2011 +0100
@@ -11,10 +11,12 @@
 import org.objectweb.asm.Label;
 import org.objectweb.asm.Opcodes;
 import org.python.core.Py;
+import org.python.core.PyException;
 import org.python.core.PyMethod;
 import org.python.core.PyObject;
 import org.python.core.PyProxy;
 import org.python.core.PyReflectedFunction;
+import org.python.core.PyString;
 import org.python.util.Generic;
 
 public class ProxyMaker implements ClassConstants, Opcodes
@@ -518,10 +520,21 @@
             callMethod(code, name, parameters, ret, method.getExceptionTypes());
             code.label(returnNull);
             code.pop();
+            throwNotImplementedException(code, name);
             doNullReturn(code, ret);
         }
     }
 
+    protected static void throwNotImplementedException(Code code, String name) {
+        code.ldc(name);
+        code.invokestatic("org/python/compiler/ProxyMaker", "throwNotImplementedException", "(Ljava/lang/String;)V");
+    }
+
+    public static void throwNotImplementedException(String name) throws PyException {
+        String msg = "abstract method \"" + name + "\" not implemented";
+        throw new PyException(Py.AttributeError, new PyString(msg));
+    }
+
     private String methodString(Method m) {
         StringBuffer buf = new StringBuffer(m.getName());
         buf.append(":");